The problems arising during the dyeing of polyacrylonitrile fibers and materials having a content thereof with cationic dyestuffs are known. Owing to their basic character, the cationic dyestuffs have a great affinity for polyacrylonitrile fibers (which are usually anionic), but they attach themselves non-uniformly thereto. This disadvantage becomes apparent particularly when it is desired to dye the fibers with bright tints. The resulting dyeings have a non-uniform or non-level appearance, which renders them unsatisfactory.
In order to obtain more uniform or level dyeings, attempts have been made to decrease the speed of absorption of the dyestuffs by careful temperature control or by addition of retardants, i.e., quaternary ammonium salts which contain higher linear or only slightly branched fatty chains, such as alkylpyridinium salts or fatty alkyltrimethyl- or fatty alkylbenzyldimethyl-ammonium salts. However, the achievement of level dyeings by retardation of the rate or speed of dyeing is extremely time-consuming. Moreover, it is unreliable because the aids used hitherto have only a specific effect and, therefore, have a relatively small range of application.